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Author Topic:   Proper Battery Form Factor or GROUP size
striper swiper posted 05-28-2009 04:17 PM ET (US)   Profile for striper swiper  
The previous owner of my boat had installed [GROUP] 27 and [GROUP] 31 [unclealr--possibly a brand] batteries. I will replace the [GROUP] 27 with a start deep cycle [GROUP] 27 size, but what about the [GROUP] 31 [size]? I have a VHF, AM, FM, tape, radio, and remember them? And an old [HUMMINBIRD SONAR]. Any recommendations [on the GROUP size of a battery to use]?
makoman310 posted 05-28-2009 05:20 PM ET (US)     Profile for makoman310  Send Email to makoman310     
[G]roup 24 cranking battery is all you need.
jimh posted 05-28-2009 08:43 PM ET (US)     Profile for jimh  Send Email to jimh     
A battery's size or form factor is normally given by its GROUP size. A GROUP 24 battery is a very common size. A GROUP 31 form factor may be a larger size. In terms of their electrical specifications, a battery is not chosen by its GROUP size. This is a physical characteristic, not an electrical characteristic.

You should select a battery on the basis of its electrical characteristics. Electrical characteristics are specifications like the marine cranking amperes (MCA), the cold cranking amperes (CCA), or the ampere-hour capacity (A-H) at a specified discharge rate. After deciding on the electrical specifications for a battery, you can look for batteries that meet the specification which are made in various sizes or form factors or GROUP numbers.

In general you can expect that the larger a battery's physical size, the greater will be its electrical specifications. However, I do not know of any way in which you can select a battery simply on its physical size. You have to consider its electrical specifications.

Also, I have no idea what you mean when you mention a battery as a "start deep cycle" battery. Batteries are generally rated as being either starting batteries or as deep cycle batteries.

striper swiper posted 05-28-2009 10:26 PM ET (US)     Profile for striper swiper    
Jim, Douglas is the brand name of the batteries.
A group 27 can be both a starter and a deep cycle.
I just wanted to know is a group 31 necessary for my 18 outrage with 150 johnson and rather basic electronics.
I'd rather have too much than too little.
HAPPYJIM posted 05-29-2009 01:55 AM ET (US)     Profile for HAPPYJIM  Send Email to HAPPYJIM     
It never hurts to have a larger battery than needed. If you have the room for it, buy the biggest you can find. If you have a 13 footer, a group 31 would be a little overkill unless your motor does not have an alternator. You may be better off with 2 group 24 batteries instead of one big 31.
HAPPYJIM posted 05-29-2009 02:02 AM ET (US)     Profile for HAPPYJIM  Send Email to HAPPYJIM     
My bad....just read you have a 18 Outrage.

My 19 Outrage II has a 2 battery set up. I like it and it is all contained in my console. Plenty of power for starting and the redundancy of 2 batteries. If you do any offshore boating, you will like having 2 batteries. If all your boating is within a mile or 2 of dry land the group 31 will do just fine.

striper swiper posted 06-07-2009 10:44 PM ET (US)     Profile for striper swiper    
I bought 2 interstate 27 deep cycle /starter batteries from the local marina

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